In assessing a patient's vascular health, it is often useful to collect diagnostic data from an interior wall of a lumen. In known intravascular diagnostic systems, a scanning catheter having a detector at its distal end is coupled at its proximal end to a motor that rotates and translates the catheter at known rates. This enables the detector to circumferentially and axially scan the interior wall, collecting diagnostic data as it does so.
Because the rates at which the catheter rotates and translates are both known, a processor receiving the diagnostic data from the detector is able to infer the location from which the diagnostic data is retrieved and to associate that location with the diagnostic data. The processor then displays a diagnostic map showing the diagnostic data as a function of location on the arterial wall.
In such a system, the scanning of the wall is driven by a motor that moves the catheter at a known rate. Hence, the position of the catheter is inferred from the known rate and the elapsed time.